Project Summary The adult brain has a remarkable capacity to recover from focal ischemic stroke (FIS). Astrocytes are the most numerous and diverse glial cells in CNS and intimately interact with neurons to support and regulate their functions. After FIS, astrocytes in the PIR exhibit dynamic changes in morphology, proliferation and gene expression especially in the peri-infarct region (PIR). These astrocytes are called reactive astrocytes (RAs). However, whether and how reactive astrocytes (RAs) affect brain recovery after FIS in the context of astrocyte?neuron interactions largely remain unexplored. In our preliminary study, we found GDNF, a potent neurotrophic factor, is dramatically upregulated in the ischemic hemisphere and RAs after photothrombosis (PT)-induced FIS. Furthermore, we found that deletion of astrocytic GDNF reduces adult neurogenesis in normal brain, and increases brain infarction and attenuates cell proliferation in the PIR after PT. Based on these strong preliminary results, we hypothesize that RAs-derived GDNF plays an important role in neural regeneration and functional brain recovery after FIS. The prohect goal is to determine whether and how RAs- derived GDNF stimulates synaptic regeneration and remodeling of surviving neurons in the PIR and improves long-term stroke outcomes after FIS. To achieve this goal, we have developed interdisciplinary technologies including self-complementary adeno-associated virus (scAAV) vectors and Glast-CreERT2:GDNFf/f mice to specifically overexpress or delete GDNF in RAs during post FIS time, in vivo two photon (2-P) long-term microscopy, electrophysiology, immunocytochemistry, Western blot (WB) analysis, brain damage and neuronal death assays and behavioral tests. We propose three specific aims. In Aim 1, we will test the hypothesis that RAs-derived GDNF can enhance synaptogenesis to stimulate neural regeneration in the PIR after FIS. We will determine the effects of RAs-derived GDNF on the expression of neuronal proteins involving synaptic function and plasticity in the PIR; using TRAP (translating ribosome affinity purification) method we will further identify neuronal transcript changes at translational status in the PIR. In Aim 2, we will test the hypothesis that RAs- derived GDNF can promote structural and functional synaptic remodeling of surviving neurons in the PIR after FIS. Using in vivo long-term 2-P imaging we will determine the effect of RAs-derived GDNF on spine turnover (i.e., spine formation and elimination), glutamate release and Ca2+ signaling in the same dendrites of surviving neurons in the PIR. We will conduct patch-clamp recording on surviving neurons in the PIR to determine the effect of RAs-derived GDNF on functional synaptic plasticity. In Aim 3, we will test the hypothesis that astrocytic GDNF can improve long-term stroke outcomes. We will evaluate the effect of RAs-derived GDNF on long-term histological and behavioral outcomes. Our project will provide novel molecular, cellular and functional insights into the brain recovery processes after FIS in the context of glia-neuron interactions, reveal potential strategies for stroke therapy, and thus has both scientific and translational significances.